[sdiy] semi-beginner's op-amp question

[Roy J. Tellason]

On Monday 04 April 2005 03:52 pm, Kevin Lightner wrote:
> Not to hijack this thread, but I have a small opamp question also.
>
> What is a good choice for an opamp for driving a long run of wire?
> Dual opamp/single supply desired, but (like many people) could go
> bi-polar or use two.
> Mostly to be used as a DC follower/driver.
> Wire is about 22ga, solid copper, unshielded. Load is basically a
> vactrol: not very picky, but about 30 ma or so, max. Obviously the
> wire adds up to something also in resistance and capacitance, but
> it's overall not a very precision circuit.
> Maybe many opamps would work, but from the general "you probably have
> these in stock" types, what would be best?
>
> Thanks for any input. :)

Much of what I've seen out there suggests that capacitive loading at the 
output of an opamp is a bad thing.  The usual remedy is to place some small 
series resistance at the output -- I've seen values of 33 and 100 ohms used.  
Whether this will work or not at 30mA of current is another matter.  You 
might want to consider using an outboard transistor to control the current, 
and including it in your feedback loop.

Is this an on-off application or does the current need to vary linearly?